annoying humming sound using LFE setting

[av addict]

hi ok just been expermenting with my gemini sub and when i use the LFE setting i get quite a annoying humming sound and it gradually fades when i turn the gain down to about 10o cloak[is this the norm}---could this be interference from my amp or cable tv ariel which goes round the back of my sub---have to experment tomorrow --if its from my amp can i take the earth cable off my plug
and use a rcd for keeping safe --- cheers find out more tomorrow